It is generally known to delimb trees by encircling the tree trunk with curved blade members and either moving the curved blade members along the length of the tree, or pulling the tree in a longitudinal direction through the curved blade members. In some cases, the delimbing device forms a part of a tree harvester and is supported for vertical movement on a track. The delimbing device moves up the track adjacent a standing tree to remove the limbs. An example of this type of delimbing device is disclosed in U.S. Pat. No. 3,183,949.
In other instances, the delimbing device is supported in a horizontal position and moves along a track while the tree is held in a horizontal position. Examples of such a tree delimbing apparatus are disclosed in U.S. Pat. Nos. 3,905,407 and 4,462,438.
U.S. Pat. No. 3,443,611 discloses a telescopic boom on which the delimbing device is attached. The telescopic boom moves the delimbing device along the length of the tree while the top of the tree is held by the inner-most portion of the telescopic boom.
U.S. Pat. Nos. 3,398,774 and 4,258,762 disclose tree delimbing apparatuses in which the limb outting head assembly is fixed in a horizontal position on a frame. The tree is then longitudinally pulled through the limb cutting head assembly by gripping jaws which are supported for movement along a horizontal track arrangement. The type of tree harvester and delimbing apparatus of the type disclosed in the patents identified above are very large and expensive and involve complicated mechanisms which are difficult to maintain in proper operating condition. Also, it is many times difficult, if not impossible, to maneuver this type of large equipment into position adjacent the particular trees to be delimbed and harvested, particularly in hilly and rough terrain.
Recognizing the problems associated with the devices disclosed in the above-identified patents, U.S. Pat. No. 4,620,578 discloses a very simple and inexpensive tree delimber adapted to be used in conjunction with a grapple equipped crane or knuckle boom loader. The delimbing device of this patent is supported in a fixed position on a trailer and includes a pair of semi-circular lower cutting blade jaws with a single semi-circular upper cutting jaw pivotally mounted between the lower jaws. The upper cutting jaw is swingable between a closed position and an open position and is maintained in engagement with the upper portion of the tree by gravity as the tree is drawn through the delimber. The delimbing device of this patent overcomes many of the problems of the large complicated devices of the other prior art, in that it is very inexpensive to construct and maintain. However, the operation of the delimber of this patent requires accurate control by the grapple crane operator to draw the tree in perfect alignment in an axial direction through the delimber throughout the entire length of travel of the tree through the delimber. If axial alignment is not accurately maintained as the tree is drawn through the fixed blades, the blades will dig into and cut the side of the tree trunk. When the blades dig into the tree trunk, the operator must reverse the direction of movement of the tree trunk to free the blades from cutting engagement therewith and then continue to pull the tree through the delimber while maintaining accurate longitudinal axial alignment with the cutting blades.